Acquisition of the GPS Clear/Acquisition (C/A) codes at low signal-to-noise ratio, such as exists inside buildings, is a difficult technical challenge for two basis reasons: (a) the amount of GPS receiver hardware needed to detect the presence of the GPS signal and acquire the C/A code (or alternatively the time needed for acquisition) becomes large as the signal-to-noise ratio decreases toward the theoretical acquisition threshold, as defined by the Shannon limit; and (b) the correlation time over which the GPS receiver is able to process the received noisy signal (which in turn sets the effective signal-to-noise ratio) is limited by the fact that the C/A code has data bit transitions that invert the C/A code, randomly, at intervals of 20 msec.
It would be useful to be able to provide an acquisition technique that addresses one or more of the problems described above. It would also be useful to be able to provide an acquisition technique that can be used by GPS receivers to improve the acquisition of signals in a disadvantaged signal environment, such as inside buildings.